Optical switch with a micro-mirror and method for production thereof

ABSTRACT

The invention concerns an optical switch using a micromirror and its method of fabrication. This optical switch comprises at least one input optical path ( 31 ) and at least a first and a second output optical path ( 35,37 ) and a micromirror ( 41 ) able to move between an output of the input optical path and inputs of the first and second output optical paths. The micromirror comprises a reflector part ( 13 ) and an actuating part ( 15 ) able to drive the reflector part in rotation. The invention applies to all areas using optical switches, and in particular the sphere of optic telecommunications.

Technical Field

The present invention pertains to an optical switch with micromirror andits method of fabrication.

More precisely, it concerns an optical switch able to transfer a lightwave conveyed by an input optical path towards a first or a secondoutput path.

The invention finds applications in all areas which use opticalswitches, and in particular the area of optic telecommunications.

Prior Art

To enable the switching of a light beam from an input optical path toany output path, there currently exist two families of switches:

-   -   one of the switch families consists of bringing the light beam        via a mechanical system able to convey said light beam (for        example a mobile beam provided with an optical guide) to the        input of one of the output optical paths; this principle is        described for example in U.S. Pat. No. 5,078,514,    -   the other switch family uses a micromirror able to move between        the input optical path and the two output optical paths so as to        enable either transmission passing of the light beam from the        input path to one of the output paths, or reflection passing of        the beam from the input path to the other output path.

The invention concerns this latter family of switches.

The interposing of micromirrors in front of an optical beam is widelyused in free space. FIGS. 1 a and 1 b and FIGS. 2 a and 2 b illustratethe use of micromirrors in free space, able to move along two positionsbetween an input fibre 1 and two output fibres 3 and 5.

In FIGS. 1 a and 1 b, the optical axis of fibre 3 lies in the opticalalignment of the axis of fibre 1, while the axis of fibre 5 isperpendicular to the axis of fibre 1.

Therefore, when the micromirror is in a position in which it is notinterposed between fibres 1 and 3 on the optical axis of said fibres,the light beam leaving fibre 1 is transmitted to fibre 3; and when themicromirror is in a position in which it is interposed between fibres 1and 3 on the optical axis of said fibres, the light beam leaving fibre 1is reflected by the mirror and is transmitted to fibre 5.

In the case shown FIGS. 1 a and 1 b, the micromirror 7 used hastranslation movement. Arrows 8 a and 8 b represent the translationmovement of the mirror in FIGS. 1 a and 1 b respectively. Thistranslation movement is made in a plane containing the plane of themicromirror.

In the case shown FIGS. 2 a and 2 b, the optical axis of fibre 3 alsolies in the optical alignment of the axis of fibre 1, while the axis offibre 5 is arranged at 45° to the axis of fibre 1. The micromirror 11used has rotational movement about a hinge 9 which is perpendicular tothe optical axis of fibre 1 and which is contained in the plane of themirror. Arrow 10 in FIG. 2 b represents the rotation movement of themirror which is able to move about 90°. Therefore, when the micromirroris below the optical axis of fibre 1, the light beam conveyed by fibre 1is transmitted to fibre 3, while when the micromirror is interposed sothat the light beam arriving from fibre 1 is 45° incident to it, saidbeam is reflected towards fibre 5.

The rigid micromirrors used in these structures are difficult totranspose to integrated optics since the fabrication technologies foroptical guides and for mirrors are different and hence not easilycompatible.

In integrated optics, known switches using the principle of light beamtransmission or reflection are obtained through the movement of twofluids (an air bubble in a liquid for example) in a recess arranged in asupport comprising optical guides forming the input and output paths,one of the fluids enables transmission of the beam and the other fluidenables its reflection. These structures raise problems of reliabilityhaving regard in particular to the movement of a fluid in a recess ofrestricted volume with problems of pollution.

Also, the rigid micromirrors used in free space are generally controlledby electrostatic forces and the electrostatic voltages required toobtain translation or rotation of the mirror must be sufficient to movethe whole mirror. The greater the size of the mirror, the higher therequired forces.

DESCRIPTION OF THE INVENTION

The present invention sets out to propose an optical switch using arigid micromirror which can be used both in integrated optics and infree space optics and therefore not having the prior art reliabilityproblems of switches in integrated optics.

A further objective of the invention is to propose an optical switchusing a micromirror able to be controlled by voltages which may be lowerthan those for previously described micromirrors.

Further objectives of the invention are to propose an optical switchusing a micromirror minimizing optical losses and able to have thefastest access time possible, and which is insensitive to polarizationand wavelength.

Finally, a further purpose of the invention is to put forward a methodfor fabricating a switch in integrated optics which is simple, easy toimplement and hence offering good production yield.

More precisely, the invention concerns an optical switch comprising atleast one input optical path, at least a first and a second outputoptical paths and a micromirror able to move between an output of theinput optical path and inputs of the first and second output opticalpaths, the input optical path and the first output optical path havingan identical optical axis, called first optical axis, and the secondoutput optical path having an optical axis called second optical axis,the micromirror comprising a reflector part and an actuating part havingan axis of rotation and able to drive the reflector part in rotationabout a plane called a tilt plane, this tilt plane being perpendicularto a plane containing the axis of rotation, and said reflector partcomprising at least one reflective face in a plane parallel to the tiltplane able to reflect a light wave derived from the input path towardsthe second output path, the first and second optical axes respectivelyforming an angle α relative to an axis of symmetry, the optical switchfurther including a control device to tilt the reflector part, thiscontrol device comprising a first set of electrodes arranged on theactuating part, a second set of electrodes arranged facing the firstset, and means for applying a potential difference between the sets ofelectrodes.

According to one particular embodiment of the invention, the opticalswitch comprises a first input optical path associated with a first anda second output optical paths, and a second input optical pathassociated with a third and a fourth output optical paths, themicromirror being able to interpose itself either between an output ofthe first input optical path and the inputs of the first and secondoutput optical paths, or between an output of the second input opticalpath and inputs of the third and fourth output optical paths.

According to the invention, the input and output optical paths arechosen independently from one another from among optical fibres oroptical guides.

Advantageously, the input and output optical paths are respectivelyoptical guides in a substrate, said substrate also including a recessable to allow rotation of the reflector part about the so-called tiltplane.

The fabrication of a switch in integrated optics using a rigidmicromirror makes it possible to overcome the prior art reliabilityproblems of switches in integrated optics.

Also, since the width of the recess is related to applied fabricationtechnologies, it can be narrow thereby minimizing the distance travelledby light waves outside the optical guides and hence minimizing opticallosses.

In addition, according to the invention, the tilt plane of the reflectorpart and the axis of rotation of the actuating part are perpendicular.The reflector part which comprises the reflective face and the actuatingpart which generally comprises a set of electrodes and forms a zone ofattraction are decoupled, which enables the micromirror of the inventionto use a lever effect which reduces the movement of the reflector part.

The movement of the micromirror generally being obtained through the useof electrostatic forces generated by two sets of electrodes to which apotential difference is applied, and since the zone of attraction isindependent from the reflector part, the surface of the electrodes ofthe actuating part can be a large surface allowing a reduction in theforces required to tilt the reflector part and hence in controlvoltages. The same applies to the inter-electrode space which may bereduced, which also enables a reduction in the forces required to tiltthe reflector part.

Angle α is advantageously non-zero.

Each set of electrodes comprises at least one electrode.

The micromirror of the invention advantageously comprises at least onelimit stop able to limit movement of the reflector part.

This limit stop, for switches with a single input path and two outputpaths for example, is in the form of a boss at one end of the reflectorpart, the width of said boss in a plane perpendicular to the tilt planeis greater than the width of the recess along the same plane.

The switch of the invention makes it possible to have rapid responsetime, in the order of a ms for example or a few dozen μs, due inparticular to the dimensions of the micromirror which may be small. Itprovides for insensitivity to polarization and wave length on account ofthe use of a transmission effect or mirror reflection effect to achieveswitching.

Evidently, the micromirror is not limited to total reflection. Thereflector part of the micromirror may allow selective reflection of onlyone polarization or only some wave lengths and respectively transmit theother polarization or other wave lengths, the micromirror then acting asfilter.

A further subject of the invention is a method for fabricating a switchof the invention in integrated optics.

This methods comprises the following steps:

-   a) in a first substrate, fabricating at least one input optical    guide, a first and a second output optical guide, a recess, and a    second set of electrodes, the input optical guide and the first    output optical guide having an identical optical axis called first    optical axis, the second output optical guide having an optical axis    called second optical axis, the first and second optical axes    respectively forming an angle α relative to an axis of symmetry (S),-   b) in a second substrate, fabricating a micromirror and a first set    of electrodes, the micromirror being able to move between an output    of the input optical guide and inputs of the first and second output    optical guides, the micromirror comprising a reflector part and an    actuating part having an axis of rotation and able to drive the    reflector part in rotation about a plane called tilt plane, this    tilt plane being perpendicular to a plane containing the axis of    rotation, and said reflector part comprising at least one reflective    face in a plane parallel to the tilt plane, able to reflect a light    wave derived from the input optical guide towards the second output    optical guide,-   c) adding the second substrate onto the first substrate so that the    micromirror is able to tilt within the recess.

Evidently, these steps may also comprise the fabrication of otherelements depending upon intended applications.

Steps a), b) and c) may be performed in this order or in differentorder. Or they may be interlinked. In particular, the adding of thesecond substrate onto the first substrate may be performed beforecomplete fabrication of the micromirror.

When the actuating part of the micromirror is conductive, this actuatingpart may then act as the first set of electrodes; the fabrication ofsaid first set is then merged with the fabrication of the actuating partof the micromirror.

According to one first embodiment, the second substrate is a stack of afirst carrier layer, a second layer and a third layer intended to formthe micromirror.

According to one advantageous embodiment, the first carrier layer is asilicon layer, the second layer is a silicon oxide layer and the thirdlayer is a silicon film, the micromirror being fabricated in said film.

Advantageously, the second substrate is a Silicon On Insulator (SOI)wafer obtained for example by adding a film of monocrystalline silicononto a silicon carrier comprising a thermal oxide layer. This siliconfilm is optionally epitaxied to desired film thickness.

Step b) of the micromirror fabrication comprises the following steps:

-   -   etching the first carrier layer and then the second layer so as        to make an opening in the substrate exposing part of the third        layer,    -   etching the third layer so as to form the patterns corresponding        to the reflective and actuating parts of said micromirror and        releasing said parts from the remainder of the third layer        allowing said layer to subsist at the axis of rotation of the        actuating part so that the micromirror remains joined to the        second substrate    -   depositing a reflective layer on all or part of a side face of        the reflector part so as to form the reflective face of the        micromirror.

If a reflector part with a limit stop is to be made, etching of thethird layer is conducted so as to obtain a pattern for the reflectorpart comprising said limit stop.

Other characteristics and advantages of the invention will be morereadily seen in the following description with reference to the appendeddrawings. This description is given solely for illustrative purposes andis non-restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a and 1 b illustrate a first example of a known switch in freespace,

FIGS. 2 a and 2 b illustrate a second example of known switch in freespace,

FIGS. 3 a, 3 b and 3 c illustrate an example of embodiment of a switchaccording to the invention in integrated optics,

FIGS. 4 a and 4 b illustrate a variant of the preceding example in whichthe micromirror comprises a limit stop,

FIG. 5 shows another example of a switch of the invention with severalinputs,

FIGS. 6 a to 6 g shows an example of embodiment of the switch in FIGS. 3a, 3 b and 3 c.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIGS. 3 a, 3 b and 3 c illustrate an example of embodiment of a switchof the invention made in integrated optics.

FIG. 3 a is an overhead view of said switch.

FIG. 3 b is a cross-section of the switch along a plane containing thereflective face of the micromirror.

FIG. 3 c is a perspective view of the micromirror used in this switch.

In a substrate S1, an input optical path 31 and two output optical paths35 and 37 are fabricated. These optical paths are formed in this exampleby optical guides.

As a general rule, an optical guide consists of a central part generallycalled the core and surrounding media positioned all around the corewhich may be identical or different. To achieve confinement of the lightin the core, the refractive index of the medium forming the core must bedifferent to and in most cases greater than those of the surroundingmedia. The guide may be a planar guide when light confinement is made ina plane containing the direction of light propagation, or a microguidewhen light confinement is made in two directions transverse to thedirection of light propagation.

To simplify the description, the guide will be likened to its centralpart or core, and only the cores of these guides are shown in all thefigures.

Also, all or part of the surrounding media shall be called “substrate”,it being understood that when the guide is not or only scarcely buriedone of the surrounding media may be outside the substrate being air forexample.

Depending upon the type of technique used, the substrate may bemonolayer or multilayer.

Also, depending upon applications, an optical guide in a substrate maybe more or less buried in this substrate and may in particular compriseportions of guide buried at varying depths. This is particularly thecase in ion exchange technology in glass. To simplify the description,the guides are shown at a constant depth in the substrate.

In FIGS. 3 a, 3 b and 3 c the optical axis of guides 31 and 37 is thesame, while the optical axis of guide 35 forms an angle 2α with theoptical axis of guide 31. Guides 31 and 35 are arranged symmetricallyrelative to an axis of symmetry S.

The output of guide 31 and the input of guide 35 firstly and the inputof guide 37 secondly are separated by a recess 39 able to allow tiltingof a micromirror 41 about a tilt plane B.

The micromirror 41 comprises a reflector part 13 and an actuating part15 having an axis of rotation 17 parallel to the axis of symmetry S; thereflector part and the actuating part being integral with one another,the actuating part is able to drive the reflector part in rotation abouta plane called a tilt plane. The tilt plane of the reflector part isperpendicular to a plane containing the axis of rotation.

The reflector part comprises at least one reflective face R in a planeparallel to the tilt plane of the reflector part. This face R is able toreflect a light wave derived from guide 31 towards guide 35.

In the figures, the reflective face is shown as a dotted line.

Therefore, when the reflector part of mirror 41 is interposed betweenthe optical axis of guide 31, the face R which then faces the output ofguide 31 and the input of guide 35 reflects the light wave derived fromguide 31 towards guide 35.

On the contrary, when the reflector part of mirror 41 is not interposedin the optical axis of guide 31, the light wave derived from guide 31 istransmitted directly via recess 9 to guide 37.

The switch further includes a control device controlling rotation of theactuating part so that the latter induces tilting of the reflector partwhich can then be interposed or not in the optical axis. This controldevice includes for example as shown in FIG. 3 b a first set ofelectrodes J1 arranged on the actuating part, a second set of electrodesJ2 arranged on the substrate, facing the first set, and means (notshown) for applying a potential difference between the sets ofelectrodes.

Each set of electrodes comprises at least one electrode. In thisexample, set J1 comprises a single electrode and set J2 comprises twoelectrodes J21 and J22 facing the electrode of set J1. Therefore, theapplication of a different potential difference between each of theelectrodes of set J2 and the electrode of set J1 makes it possible tiltthe reflector part towards the electrode of set J2 for which thepotential difference is the greatest.

Hence two positions may be defined:

-   -   a first position (shown FIG. 3 b) in which one end of the        reflector part moves down into recess 9 through the        electrostatic forces between electrodes J1 and J21; the        reflective face covering at least this end then intercepts the        light wave (shown as an ellipse L on surface R) and enables        reflection of said wave, and        -   a second position in which the end of the reflector part            moves up out of recess 39 through the electrostatic forces            between electrodes J1 and J22, the reflective face no            longer-intercepts the light wave which is therefore            transmitted.

The reflector part of the micromirror has a side face which is fully orpartly reflective; the part of the side face able to reflect is thereflective face. In FIGS. 3 b and 3 c, the side face is entirelyreflective and merges with the reflective face, but evidently only thatpart (effective part) of this side face intended to be intercept theoptical axis could have been reflective.

The actuating part (see FIGS. 3 a and 3 c) is formed by a central zoneon which electrode J1 is arranged whose dimensions are close to thedimensions of the central zone, and by a narrower zone either side ofthe central zone arranged along the axis of rotation to connect thecentral zone to a rigid structure. This narrower zone forms a hinge forthe actuating part.

In this example of embodiment of a switch in integrated optics, therigid structure to which the mobile part is joined consists of a secondsubstrate S2 arranged on substrate 1.

In the invention, the reflector part is able to move along the tiltplane perpendicular to a plane containing the axis of rotation 17 of theactuating part. The latter enables tilting of the reflector part under alever effect. The effective part of the reflective face may, on thisaccount, be distanced away from the axis of rotation and theinter-electrode space may be small (for example a few μm).

FIGS. 4 a and 4 b show a variant of embodiment of a micromirror of aswitch in integrated optics, FIG. 4 a is a perspective view of themicromirror and FIG. 4 b is an underside view of the mirror.

This micromirror, as previously, comprises an actuating part 15 and areflector part 13. These parts are the same as those described withreference to FIGS. 3 a to 3 c with the exception that the reflector partalso comprises a limit stop 23 at one of its ends opposite the endhaving the effective part of the reflective face.

This limit stop limits the movement of the reflector part outside therecess. In this way, it particularly enables locking of the micromirrorin a position in which the reflector part is not interposed in front ofthe optical beam.

The limit stop consists for example of a boss at the end of thereflector part; the width of said boss in a plane perpendicular to thetilt plane is greater than the width of the recess along this sameplane.

By way of indication, the form of recess 49 along this plane is shown asa dotted line.

FIG. 5 shows another example of a switch of the invention in integratedoptics from an overhead view. This switch comprises the same elements asFIG. 3 a and in particular a first input guide 31 associated with afirst output guide 35 and with a second output guide 31, but it alsoincludes a second input guide 31′ associated with a third and fourthoutput optical guide 35′ and 37′. Guides 31′ and 35′ are positionedsymmetrically relative to an axis of symmetry S′ and with this axisrespectively form an angle β.

The reflector part 13 of the micromirror is able to interpose itselfeither between the output of the first input optical guide and theinputs of the first and second output optical guides, or between theoutput of the second input optical guide and the inputs of the third andfourth output optical guides.

Therefore, when the light beam conveyed by guide 31 is reflected towardsguide 35, the light beam conveyed by guide 31′ is transmitted to guide37′. Similarly, when the light beam conveyed by guide 31 is transmittedto guide 37, the light beam conveyed by guide 31′ is reflected towardsguide 35′.

FIGS. 6 a to 6 g illustrate an example of embodiment of the switch shownFIGS. 3 a to 3 c. FIGS. 6 a to 6 d are cross-sections along a planeparallel to the tilt plane and show the fabrication of the micromirrorin a substrate S2, FIG. 6 e shows the preparation of substrate S1comprising the optical guides and FIGS. 6 f and 6 g are cross-sectionsin a plane perpendicular to the tilt plane of the switch after addingthe micromirror onto substrate S1.

In FIG. 6 a a substrate S2 is shown which, in this example, is formed bya wafer of SOI type which corresponds to a stack of three layers: asilicon layer 50, a silica layer 51 and a thin film of advantageouslymonocrystalline silicon 52.

Etching was performed in silicon layer 50 then in silica layer 51 toobtain an opening 33. Etching of layer 50 may be made along preferentialcrystallographic planes using the silica layer as stop layer; thisetching is anisotropic chemical etching for example of KOH type so as toobtain an opening of conical shape, and etching of layer 51 may beperformed using dry anisotropic etching of reactive ion etching typeusing fluorinated gases.

The silica layer could have been maintained in opening 33.

FIG. 6 b shows an epitaxy step of silicon film 52; this step enablesadaptation of the thickness of the silicon layer to the desiredthickness of the micromirror to be fabricated. Evidently, if the initialthickness of film 52 is sufficient, this epitaxy is not necessary.

By way of example, the thickness of silicon layer 54 obtained afterepitaxy lies between 5 and 50 μm for example depending upon themechanical characteristics and the reflective surface involved.

FIG. 6 c shows the fabrication of the micromirror by etching layer 54 inan appropriate pattern.

To achieve this two etchings are conducted, for example:

-   -   a first etching to hollow out the central part of the        micromirror,    -   a second etching to release the micromirror from the remainder        of layer 54 (the actuating part is only joined to layer 54 by        the narrow zone corresponding to the hinge of the actuating        part).

The first etching must be conducted starting from the face of film 54opposite the face present in opening 33. This etching is made through anappropriate mask (not shown) and in particular enables thinning of film54 outside the zones intended to form the two ends E1 and E2 of thereflector part.

The second etching can be made starting from either one of the faces oflayer 54. The mask (not shown) used for this etching must allow etchingof layer 54 over its entire remaining thickness so as to obtain thecontour of the micromirror, i.e. the reflector part and the mobile partsuch as shown in the overhead view in FIG. 3 a or FIG. 4 b in which alimit stop is used.

The first and second etchings are chosen independently from one anotherfrom among anisotropic chemical etching for example with a KOH solutionor dry anisotropic etching, for example reactive ion etching using SF₆fluorinated gases.

With these etchings it is possible to obtain good surface quality sincethey are used to fabricate the side face of the micromirror.

After this step, as shown FIG. 6 d, on the reflector part or at least onthe side face, a reflective material is deposited such as aluminium orgold or even dielectric multilayers deposited by cathode vapour orsputtering. In this manner the reflective surface of the micromirror isfabricated. Also, a conductive deposit is made in the hollowed out partof the micromirror, more precisely underneath the mobile part using apattern such as shown in perspective in FIG. 3 c. This gives electrodeJ1. This conductive deposit is made for example by depositing a layer ofmetallic material such as aluminium, gold, chromium, etc. then etchingthis layer. At the same time as this electrode is formed, the electricalconnection (not shown) of this electrode to supply means is also made.

If layer 54 is itself conductive as is the case with silicon, then thisconductive deposit is not necessary and that part of layer 54corresponding to the actuating part itself forms the electrode.

FIG. 6 e shows a cross-section of substrate S1 along a plane containinginput guide 31 and output guide 37. The optical guides may be made inthe substrate using any integrated optics technique, and in particularusing ion exchange techniques in glass, or silica depositing techniqueson silicon or on glass or on fused silica.

A recess 39 is also made in the substrate, with a glass substrate forexample this recess may be obtained by chemical type etching usinghydrofluoric acid through a mask (not shown).

For a silica or semiconductor substrate, this recess is preferably madeusing dry anisotropic etching so as to obtain etch flanks having verygood perpendicularity relative to the surface of the substrate.

This recess may also be made by mechanical sawing such aspolishing-sawing.

Also, on the surface of S1 (before or after forming the recess) aconductive deposit is made which is etched to obtain electrodes J12 andJ22 of set J2.

This deposit is a layer of metallic material for example such asaluminium or gold, chromium deposited by cathode vapour or sputteringand etched by chemical etching or reactive ion etching so as to obtainthe two electrodes J21 and J22. At the same time as this electrode ismade, the electric connections (not shown) of these electrodes to supplymeans are also made.

FIGS. 6 f and 6 g illustrate the switch of the invention after addingsubstrate S2 onto substrate S1 so that the micromirror lies opposite therecess and in particular so that the reflector part may have a tiltingmovement within this recess.

In FIG. 6 f, the reflector part of the micromirror is in top position,in other words the reflective surface does not intercept the opticalaxis of guides 31 and 37, and the light beam conveyed by guide 31 istransmitted directly via recess 39 to guide 37.

In FIG. 6 g, the reflector part of the micromirror is in bottomposition, in other words the reflective face in recess 39 intercepts theoptical axis of guide 31 and the light beam conveyed by guide 31 isreflected by the reflective face towards guide 35 which does not lie inthe cross section of FIG. 6 g.

Adding substrate S2 onto substrate S1 may be made using any knowntechnique, in particular by molecular bonding or any appropriatecementing technique (a bead of polymer cement for example) or further bybrazing.

A stack of substrate S2 such as shown in FIG. 6 a may also be made usinga silicon carrier on which thermal oxidation is conducted to form thesilica layer and finally a deposit of polycrystalline silicon ofsuitable thickness to fabricate the micromirror.

In this example of embodiment, substrate S2 is added onto substrate S1after fabrication of the micromirror; evidently, substrate S2 may beadded onto substrate S1 before the fabrication of said micromirror or atleast before its release so that this addition can be conducted with amechanically more rigid structure.

The examples of embodiment previously described concern switches inintegrated optics using optical guides. Evidently, as seen above, theswitch of the invention may be made in free space. In this case, theinput and output guides are optical fibres which may be arranged in asubstrate in which rails have been cut (“V” grooves for example) to holdsaid fibres in position. A recess for movement of the micromirror mayalso be provided between the ends of the fibres. The micromirror may, asfor the case in which optical guides are arranged on an independentsubstrate, be added onto the substrate of fibres.

1. An optical switch comprising: a first input optical path; a first anda second output optical paths; a control device; and a micromirrormovable between an output of the first input optical path and inputs ofthe first and second output optical paths, the first input optical pathand the first output optical path having an identical first opticalaxis, and the second output optical path having a second optical axis,the first and second optical axes respectively forming an angle relativeto an axis of symmetry, wherein the micromirror comprises: a reflectorpart and an actuating part, the actuating part having an axis ofrotation, the actuating part being configured to drive the reflectorpart in rotation about a tilt plane, the tilt plane being substantiallyperpendicular to a plane containing the axis of rotation, and thereflector part including a reflective face in a plane substantiallyparallel to the tilt plane, the reflective face being configured toreflect a light wave coming from the first input path towards the secondoutput path, wherein the control device is configured to tilt thereflector part, the control device comprising a first set of electrodesarranged on the actuating part, a second set of electrodes facing thefirst set of electrodes, the first and second set of electrodes adaptedto having a potential difference applied thereacross.
 2. An opticalswitch as in claim 1, further comprising a second input optical pathassociated with a third and fourth output optical paths, wherein themicromirror is configured to interpose between one of an output of thefirst input optical path and inputs of the first and second outputoptical paths and between an output of the second input optical path andinputs of the third and fourth output optical paths.
 3. An opticalswitch as in claim 1, wherein the first optical path and the first andsecond output optical paths are selected from the group comprisingoptical fibres and optical guides.
 4. An optical switch as in claim 1,wherein the first input optical path and the first and second outputoptical paths are optical guides in a first substrate, said firstsubstrate comprising a recess configured to allow the reflector part torotate about the tilt plane.
 5. An optical switch as in claim 1, whereinthe angle is different from zero.
 6. An optical switch as in claim 1,wherein each set of electrodes comprises at least one electrode.
 7. Anoptical switch the micromirror comprises at least one limit stopconfigured to limit a movement of the reflector part.
 8. An opticalswitch as in claim 7, wherein the limit stop is formed by a bossdisposed at one end of the reflector part, and the width of the boss ina plane substantially perpendicular to the tilt plane is greater thanthe width of a recess along the same plane.
 9. A method for fabricatingan optical switch, comprising: fabricating, in a first substrate, afirst input optical guide, a first and a second output optical guides, arecess and a second set of electrodes, the first input optical guide andthe first output optical guide having an identical first optical axis,the second output optical guide having a second optical axis, the firstand the second optical axes respectively forming an angle δ relative toan axis of symmetry; fabricating, in a second substrate, a micromirrorand a first set of electrodes, the micromirror being movable between anoutput of the input optical guide and inputs of the first and secondoutput optical guides, the micromirror comprising a reflector part andan actuating part having an axis of rotation, the actuating part beingconfigured to drive the reflector part in rotation about a tilt plane,the tilt plane being substantially perpendicular to a plane containingthe axis of rotation, and the reflector part comprising at least onereflective face in a plane substantially parallel to the tilt plane, thereflective face being configured to reflect a light wave coming from thefirst input optical guide towards the second output optical guide; andadding the second substrate onto the first substrate so that themicromirror is tiltable within the recess.
 10. A method for fabricatingan optical switch as in claim 9, wherein the second substrate is a stackof a first carrier layer, a second layer and a third layer.
 11. A methodfor fabricating an optical switch as in claim 10, wherein the firstcarrier layer is a layer of silicon, the second layer is a layer ofsilicon oxide and the third layer is a silicon film, the micromirrorbeing fabricated in the silicon film.
 12. A method for fabricating anoptical switch as in claim 11, wherein the silicon film is amonocrystalline silicon film.
 13. A method for fabricating an opticalswitch as in claim 10, wherein fabricating, in a second substrate, themicromirror and the first set of electrodes, comprises: etching thefirst carrier layer and etching the second layer so as to make anopening in the second substrate exposing part of the third layer;etching the third layer so as to form patterns corresponding to thereflector part and the actuating part of the micromirror, and so as torelease the reflector and actuating parts from the remainder of thethird layer to allow the third layer to subsist at the axis of rotationof the actuating part so that the micromirror remains joined to thesecond substrate; and depositing a reflective layer on at least aportion of a side face of the reflector part so as to form thereflective face of the micromirror.
 14. A method for fabricating anoptical switch comprising: etching a first layer and a second layer of asubstrate so as to make an opening in the first layer and the secondlayer to expose an area of a third layer of the substrate; etching thethird layer to form a micromirror comprising a reflector part and anactuating part such that the reflector part and the actuator part arereleased from a remainder of the third layer and a portion of the thirdlayer forms a hinge connecting the actuator part to the third layer; anddepositing a reflective layer on a surface of the reflective part toform a reflective surface of the micromirror.
 15. A method forfabricating an optical switch as in claim 14, wherein the actuating partis configured to rotate the reflector part around a rotation axis of thehinge portion.
 16. A method for fabricating an optical switch as inclaim 14, wherein the reflector part is rotatable about a tilt planesubstantially perpendicular to a plane containing the rotation axis ofthe hinge portion and the reflective surface of the reflector part is ina plane substantially parallel to the tilt plane.
 17. A method forfabricating an optical switch as in claim 14, wherein the first carrierlayer is a layer of silicon, the second layer is a layer of siliconoxide and the third layer is a silicon film.
 18. A method forfabricating an optical switch as in claim 14, further comprising:fabricating an input optical guide, a first output optical guide, asecond output optical guide, and a recess in a support substrate suchthat the first input optical guide and the first output optical guidehave a common first optical axis, the second output optical guide has asecond optical axis and the first and second optical axes form an angle.19. A method for fabricating an optical switch as in claim 18, furthercomprising depositing the substrate from which the micromirror is formedon the support substrate from which the optical guides are fabricatedsuch that the micromirror is tiltable within the recess.
 20. A methodfor fabricating an optical switch as in claim 19, wherein the reflectivepart of the micromirror is movable between an output of the inputoptical guide and inputs of the first and second output optical guides.